How Many Fish Need to Be Measured to Effectively Evaluate Trawl Selectivity?

Area of Science:

• Fisheries Science
• Marine Biology
• Quantitative Ecology

Background:

• Trawl selectivity assessments require accurate fish sampling data.
• Uncertainty in selectivity parameters can impact fisheries management.
• Standardized guidelines for sampling effort are needed by practitioners.

Purpose of the Study:

• To provide guidelines on necessary fish sampling effort for trawl selectivity sea trials.
• To determine the number of fish measurements needed to achieve specific uncertainty levels for selectivity parameters.
• To investigate how experimental methods and catch size structure influence uncertainty.

Main Methods:

• Simulated data from Barents Sea cod and Mediterranean red mullet fisheries were used.
• Analysis focused on the relationship between fish sample size and uncertainty in selection parameters.
• Comparison of sampling effort between covered codend and paired-gear methods.

Main Results:

• Uncertainty in selection parameters decreases with an increasing number of measured fish, following a power model.
• The covered codend method requires significantly less sampling effort than the paired-gear method.
• In some cases, the paired-gear method requires up to 10 times more measured fish for the same uncertainty level.

Conclusions:

• Guidelines for fish sampling effort in trawl selectivity studies can be generalized across fisheries.
• The covered codend method is more efficient in reducing uncertainty for a given sampling effort.
• Practitioners can use these findings to optimize sea trial designs and data collection strategies.